Methods and systems for authenticating a user. One system includes a camera and an authentication computer. The authentication computer is configured to receive an image of a user captured by the camera, determine, based on the image, a constraint of the user impacting an availability of a part of the user's body for use in authenticating the user, and determine, based on the constraint of the user, an action to be performed by the user. The authentication computer is also configured to transmit data to a user device worn by the user, the data usable by the user device to output instructions to the user to perform the action, and, in response to detecting the action performed by the user, authenticating the user to use a resource.